Numerous polymer-based medical devices have been developed for implantation or insertion into the body. For example, in recent years, drug eluting coronary stents, which are commercially available from Boston Scientific Corp. (TAXUS and PROMUS), Johnson & Johnson (CYPHER) and others, have been employed for maintaining vessel patency. These existing products are based on metallic expandable stents with biostable polymer coatings, which release antiproliferative drugs at a controlled rate and total dose. Specific examples of biostable polymers for biostable drug eluting polymer coatings include homopolymers and copolymers, such as poly(ethylene-co-vinyl acetate), poly(vinylidene fluoride-co-hexafluoropropylene) and poly(isobutylene-co-styrene), for example, poly(styrene-b-isobutylene-b-styrene) triblock copolymers (SIBS).
Neurostimulation devices are a known class of medical device, which deliver mild electrical impulses to neural tissue. For example, electrical impulses may be directed to specific sites to treat pain, Parkinson's disease or epileptic seizures, or to enhance sensory function. Specific examples of neurostimulation systems include spinal cord stimulation (SCS) systems, deep brain stimulation (DBS) systems, peripheral nerve stimulation (PNS) systems, cochlear implant systems, retinal implant systems, implantable pacemaker systems, and implantable cardioverter-defibrillators (ICD's). Each of these systems includes a neurostimulator and one or more electrical leads, each containing one or more contacts.
As used herein, a stimulation “lead” is an implantable device that has one or more electrical contacts that deliver current to tissue to be stimulated. A “contact” is a part of the lead which is electrically conductive and is in contact with the body tissue that is to be stimulated. The terms “lead” and “electrode” may be used interchangeably herein and refer to the entire elongate structure that is partially or wholly implanted into the patient. A stimulation lead can include, for example, one or more contacts, an insulating body (also referred to herein as a “lead body”), one or more elongate conductors (e.g., wires) running within at least a portion of the length of the lead body, and any other assembly on or within the lead body. The lead body is typically formed from a polymeric material.
Systems for SCS and DBS generally include a neurostimulator and one or more stimulation leads. Commonly the neurostimulator is an implantable pulse generator (IPG), which holds advanced electronics and a rechargeable battery and generates pain-masking electrical signals.
SCS is a safe and effective therapy that has been in use for over several decades and has helped thousands of people find pain relief. SCS devices may be totally or partially implantable. Commonly, at least the IPG and stimulation lead(s) are implantable. For instance, an IPG may be implanted in the abdomen, upper buttock, or pectoral region of a patient, whereas at least one lead may be implanted under the skin next to the spinal cord. Each lead may contain one or more contacts (e.g., from one to eight contacts or more) that deliver pain-masking electrical signals to the spinal cord. In certain systems, one or more lead extensions are used to electrically connect the stimulation lead to the IPG, which lead extensions may also be implantable.
A DBS device comprises similar components (i.e. an IPG, at least one stimulation lead, and commonly at least one lead extension) and may be utilized to provide a variety of different types of electrical stimulation to reduce the occurrence and/or effects of Parkinson's disease, epileptic seizures, or other undesirable neurological conditions. In this case, the IPG may be implanted, for example, into the pectoral region of the patient and the lead(s) implanted in the brain. One or more lead extensions may be implanted and extend along the patient's neck so as to electrically connect the stimulation lead(s) to the IPG. The distal end of the lead(s) may contain one or more contacts (commonly from four to eight contacts).
The implantation procedures for SCS and DBS devices are reversible, which means even though they are surgically implanted, the devices can be removed by the doctor.
An example of a neural stimulation system 10 which may be used for SCS and/or DBS is shown in FIG. 1. Such a system typically comprises an IPG 12, a lead extension 14, a lead 16 having a contact array 18 including a plurality of contacts 17. The IPG 12 is provided with a connector 5, which accepts the connector end of the lead extension 14. The contacts 17 are arranged as shown in an in-line contact array 18 near the distal end of the lead 16. Other contact array configurations may also be used, such as non-linear and parallel configurations, among others. The IPG 12 generates current pulses that are applied to selected ones of the contacts 17 within the array 18. See Pub. No. US 2007/0168007 to Kuzma. A lead 16 like that shown in FIG. 1 may be made in the following manner, among other methods: Individually insulated wires may be placed loosely within polymer tubing such as silicone, polyurethane, or polytetrafluoroethylene tubing. A platinum contact may be welded at the distal end of each wire, and a controlled spacing may be provided between each contact. Voids between the contacts are then filled with a suitable polymer, such as silicone or polyurethane, using known injection molding techniques. See Pub. No. US 2007/0168004 to Walter.
A cochlear implant system is an implantable electronic device for a patient with severe to profound deafness (e.g., 60-120 dB or more of hearing loss) caused by a sensory deficiency. It has an external component and an internal component that work in concert. The external component typically comprises an externally worn microphone, a sound processor, and a transmitter. The internal component typically comprises a receiver, a neurostimulator, and a neurostimulation lead with one or more electrical contacts (typically 16-24 electrical contacts) that is implanted within a patient's inner ear. In a normal ear, sound waves enter the external ear, vibrate the flexible surface of the eardrum and middle ear bones, and convey sound to the oval window of the inner ear or cochlea. In the cochlea, the vibration is transmitted to the perilymph fluid, causing movement of the hair cells in the cochlea, which convert the motion to electrical signals and transmit the signals to the auditory nerve. In a person with sensory hearing loss, these hair cells may be damaged and unable to transmit the electrical signal to the auditory nerve. A cochlear implant such as that previously described can replace the function of the hair cells, receiving the sound and converting it to an electrical signal to send to the auditory nerve.
FIG. 2 depicts the distal end of one type of a lead 46 that can be used with an implantable cochlear stimulation system. In this example, the lead 46 includes an in-line configuration of sixteen contacts, designated E1, E2, E3, . . . E16 disposed at the surface of a polymeric lead body. Electrical contact E1 is the most distal electrical contact, and electrical contact E16 is the most proximal. The more distal electrical contacts, i.e., the electrical contacts having lower numbers such as E1, E2, E3, E4, are the electrical contacts through which stimulation pulses are applied in order to elicit the sensation of lower perceived frequencies. The more proximal electrical contacts, i.e., the electrical contacts having higher numbers such as E13, E14, E15 and E16, are the electrical contacts through which stimulation pulses are applied in order to elicit the sensation of higher perceived frequencies. The particular electrical contact, or combination of electrical contacts, through which stimulation pulses are applied is determined by the speech processing circuitry, which circuitry, inter alia, and in accordance with a selected speech processing strategy, separates the incoming sound signals into frequency bands and analyzes how much energy is contained within each band, thereby enabling it to determine which electrical contacts should receive stimulation pulses. See, e.g., Pub. No. US 2005/0251225 to Faltys et al.